The present invention relates generally to the field of percutaneous transluminal treatment of stenosed or narrowed arteries in the human vascular system. More specifically, the invention is directed to a sheath for delivering intravascular filters for use in capturing embolic debris across tight lesions.
Arteries can become stenotic in a number of ways. Often, a stenosis or lesion forms due to an accumulation of atherosclerotic plaque on the walls of a blood vessel. Atherosclerotic plaque is typically a hard calcified substance, particles of which may dislodge during interventional procedures and flow freely in the circulatory system. A stenosis also may form from an accumulation of thrombus material which is typically softer than atherosclerotic plaque, but can nonetheless cause restricted blood flow in the lumen of a vessel. Like atherosclerotic plaque, thrombus material may sometimes dislodge during interventional procedures. Free flowing particulates, whether composed of plaque or thrombus material, are commonly referred to as emboli. Such free flowing emboli are dangerous since they may become lodged in small blood vessels and occlude or partially occlude the vessels.
Various approaches have been developed to treat a stenotic lesion in the vasculature. One of the most common is balloon angioplasty. Balloon angioplasty is directed towards relieving the constriction in the artery by radially expanding the stenosis to increase the diameter of the artery wall at the region of the stenosis. Another common procedure used to treat a stenotic lesion is atherectomy. In an atherectomy procedure, the stenosis is removed from the artery by the action of a cutting blade.
In a typical balloon angioplasty procedure, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the femoral artery by means of a conventional Seldinger technique and advanced within a patient""s vascular system until the distal end of the guiding catheter is positioned at a point proximal to the lesion site. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient""s vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the lesion. Once in position, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at a relatively high pressure to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall, thereby dilating the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter may be withdrawn from the patient""s vasculature and blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
The procedure for atherectomy is similar to that of balloon angioplasty in that a guiding catheter is introduced into the patient""s vasculature through a conventional Seldinger technique and a guide wire is typically advanced through the guiding catheter and across an arterial lesion to a point distal of the lesion. However, rather than expanding the lesion and artery with a balloon as in angioplasty, in atherectomy, a specialized catheter containing rotating cutting blades is used to mechanically cut or abrade the stenosis from the wall of the artery.
With either of the above procedures, the treated artery wall suffers a degree of trauma and in a small percentage of cases may abruptly collapse or may slowly narrow over a period of time. To prevent either of these conditions, the treatment procedure may be supplemented by implanting within the arterial lumen a prosthetic device known as a stent. A stent is a small tubular metallic structure which is fitted over a catheter balloon and expanded at the lesion site. Stents serve to hold open a weakened blood vessel and help to prevent the blood vessel from collapsing or narrowing over time.
Balloon angioplasty, atherectomy, and stenting procedures have proven successful and are widely used in the treatment of stenosis of the coronary arteries and have, for many patients, rendered unnecessary invasive bypass surgery. However, all of the above procedures may create embolic particles which in certain critical arteries, such as the carotid arteries, may pose a significant risk of ischemic stroke. For this reason, these beneficial techniques have not been widely used in treating stenosis of the carotid arteries, leaving invasive bypass surgery as the primary treatment of choice.
Embolic particles may be created during balloon angioplasty because stenoses are often formed from hard calcified plaque which tends to crack when subjected to radial expansion of the inflatable balloon. Upon cracking, emboli may be released into a patient""s bloodstream. Emboli may also be formed during a stenting procedure since the metal struts of the stent may cut into the stenosis and shear off plaque or thrombus material. During an atherectomy procedure, a constant stream of particles is cut from the stenosis. Typically, a suction catheter is used to capture these particles before the particles flow downstream in the vessel. However, it is often necessary to pull a high vacuum in order to remove all debris created by the cutting process. In some circumstances, it is not possible to pull a high enough vacuum to remove all debris without causing radial collapse of the weakened artery. Thus, some particles may not be drawn into the suction catheter and may flow downstream as emboli, where the particles may become lodged in small diameter blood vessels.
Numerous embolic filters or traps have been proposed, to capture embolic particles flowing distal of a lesion. The majority of these devices use some form of woven mesh basket. Some of these devices are self-expanding and are intended to be attached to a guide wire and delivered by a catheter or delivery sheath. Once the filter is in position in the vasculature, the sheath is removed from the collapsed filter to allow the filter to self-deploy to an expanded position within an artery. A typical example of the wire mesh basket type of intravascular filter is described in U.S. Pat. No. 4,873,978, entitled xe2x80x9cDevice and Method for Emboli Retrievalxe2x80x9d issued to Ginsburg. Ginsburg discloses a removable vascular filter permanently attached to a guide wire for deployment from a catheter. The filter is comprised of an expandable wire mesh basket employing diamond shaped cells. Upon deployment, the filter expands to contact the walls of the lumen, thereby obstructing the vessel and straining blood flowing through the lumen.
One problem common to most types of intravascular filters is the process of delivering the filter to a point distal of the lesion without creating embolic particles prior to the filter""s deployment. In delivering an intravascular filter, typically, a guiding catheter will have been previously advanced through the patient""s vasculature to a point proximal of the arterial lesion. Subsequently, the filter along, with a delivery sheath which covers the collapsed filter, is advanced through the guiding catheter and across the arterial lesion. Then the sheath may be retracted to deploy the filter. Since arterial lesions tend to be formed of friable material, sufficient abrasion of the lesion caused by the delivery sheath while crossing the lesion or by any subsequent manipulation process required to deploy the filter may create embolic particles.
What is needed therefore is a delivery sheath with a sufficiently low profile that it may cross a lesion without causing any significant abrasion, which may lead to the creation of embolic particles. In addition, the sheath should have a soft and flexible distal tip to reduce trauma to the lesion in the event of contact during crossing and to reduce possible abrasion during deployment of the filter. Further, the filter should include features that allow for rapid deployment of the filter with a minimum of relative motion between the delivery sheath and the guide wire. The present invention meets these and other needs.
The present invention provides a delivery sheath for deploying collapsible intravascular filters. The delivery sheath includes a stiff proximal portion to help advance the sheath through a guiding catheter, and along a guide wire, and a soft distal tip for holding and delivering a deployable filter to a location distal of an arterial lesion. The proximal portion is produced from a material having relatively high stiffness, thereby giving the proximal portion high column strength which results in good pushability of the delivery sheath through tortuous vessels. The distal tip of the sheath is made from a softer, more pliable material than that of the proximal portion. The distal tip has a relatively low stiffness which minimizes trauma to the vessel caused by contact between the vessel and the distal tip. In addition, the distal tip is necked down from the proximal portion to form a reduced crossing profile. The reduced profile decreases the likelihood that the distal tip will contact an arterial lesion, while crossing the lesion, and consequently reduces the possibility that plaque will be abraded or sheared from the surface of the lesion.
In order to aid a vascular surgeon in placing the sheath under fluoroscopy or similar x-ray visualization procedures, the distal tip may be made radiopaque by molding the tip from a polymer material containing radiopaque particles, such as bismuth particles, held in suspension in the polymer. Alternatively, the distal tip may be equipped with radiopaque markers. The distal tip may be co-molded with the proximal portion to form a single unitary delivery sheath or the distal portion may be formed as a separate component which is attached to the proximal portion of the sheath by adhesives, ultrasonic welding, or other suitable bonding methods.
Abrasion between the sheath and the lesion during sheath introduction and filter deployement may be minimized by reducing the relative motion between the distal tip and the guide wire. This may be accomplished by partially loading the filter device within the distal tip. In partial or half-loading, about one half of the length of the filter device is loaded into the distal tip, while the remainder, typically the filtering element, is left extending from the tip. Particular embodiments of the distal tip incorporate profiled cavities having positive stop features for facilitating half-loading of the filter. A filter device which is half-loaded into the delivery sheath requires only about one half of the relative motion between the sheath and the guide wire for deployment that would otherwise be required by fully loading the filter within the delivery sheath. Thus, half-loading the filter device is advantageous in that it allows for quick filter deployment with minimal manipulation needed for deployment, as well as minimal force.
The present invention reduces the likelihood of emboli formation during the delivery of an intravascular filter by providing a delivery sheath with a radiopaque, low profile, distal tip which minimizes the possibility of abrasion and shearing of the lesion as the sheath crosses a tight lesion. Thus, the delivery sheath of the present invention increases the safety and efficacy of interventional procedures. Other features and advantages of the invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.